It is well-known that lead-containing brass alloys such as CuZn40Pb1, C36000, C3604 and C3771 usually contain 1.0-3.7 wt % Pb for ensuring excellent free-cuttability.
Lead-containing brass alloys are still widely used in the manufacture of many products due to their excellent cuttability and low cost. However, Pb-contaminated steam produced by the process of smelting and casting lead-containing brass alloy, and Pb-contaminated dust produced in the process of cutting and grinding the lead-containing brass alloy, are harmful to the human body and the environment. If the lead-containing brass alloys are used in drinking-water installations such as faucets, valves and bushings, contamination of the drinking water by Pb is unavoidable. In addition, toys which are produced by Pb-containing brass alloys are more harmful, as they are touched frequently, thus increasing potential exposure to Pb.
Ingestion of lead by humans is harmful, so the use of lead is being strictly banned by law in many countries due to concerns for health and the environment. For dealing with this challenge, metallurgists and manufacturers of copper materials actively research and develop lead-free free-cutting brass alloys. Some of them use Si instead of Pb, but the cuttability is not remarkably improved and the cost increases due to the high quantity of copper. Therefore, silicon brass alloys are not commercially competitive at present. One commonly used type of lead-free free-cutting brass alloy is a bismuth brass alloy, which uses bismuth instead of Pb. Many kinds of bismuth brass alloys with high or low zinc contents have been developed, and their formal alloy grades have been registered in the United States. These kinds of brass alloys contain valuable tin, nickel and selenium, as well as bismuth. Although their cuttability is 85%-97% of lead-containing brass alloy C36000, their cost is far higher than lead-containing brass alloy C36000. Therefore, these kinds of bismuth brass alloys are not competitively priced. Bismuth brass alloys also have been researched and developed in Japan and China, and applications filed in their Patent Offices. Considering that bismuth is expensive, rare in the reserves and has poor cold and hot workability, using a bismuth brass alloy instead of a lead-containing brass alloy may be financially problematic. The invention of a free-cutting antimony brass alloy which uses Sb instead of Pb has been patented in China (ZL200410015836.5). A corresponding U.S. (US2006/0289094) application is currently pending.